Recent developments in eco-efficient bio-based adhesives for wood bonding: opportunities and issues

Recent developments and trends in the field of eco-efficient bio-based adhesives are reviewed. Eco-efficient means efficient with regard to both ecological and economical aspects. The recent developments in tannin adhesives without the use of any aldehyde-yielding compounds under the conditions of use, or even without the use of any hardeners, are described. Lignin adhesives are discussed next. Developments in protein adhesives, particularly the recent development in soy protein adhesives, are then addressed. Several new trends in carbohydrate adhesives, namely as modifiers of existing adhesives, by forming degradation compounds such as furanic compounds which can then be used as adhesives building blocks, and directly as wood adhesives, even in the form of liquified wood, are addressed. Unsaturated oil adhesives based on epoxidized unsaturated vegetable oils are also described, as well as an example of cashew nut shell oil modified by a new and inexpensive method of ozonolysis to yield an adhesive by self-condensation of the material. The review addresses last the new process of solid wood welding by mechanical friction without the use of any adhesive, in which the wood interfacial region itself is used as the binder.